Malicious Office (OOXML) / .XLSX — malware analysis report

Static analysis result for SHA-256 f92bc788bcf8eaf0…

MALICIOUS

Office (OOXML) / .XLSX

24.5 KB Created: 2006-09-16 00:00:00 UTC Authoring application: Microsoft Excel 14.0300
MD5: 4c7cd66e78f1878d947a0db1da9b4162 SHA-1: e2b520521e1042803c1a19d64388d06806a69584 SHA-256: f92bc788bcf8eaf09d1a67f25045cb63d7f54aaf40f9e4838bf663f264be7181
120 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Visual Basic T1204.002 Malicious File

The sample is an Excel file containing Excel 4.0 macros, as indicated by the OOXML_XLM_MACROSHEET heuristic. The OOXML_XLM_BINARY_WINAPI_STRINGS heuristic reveals strings related to downloading and executing files, such as URLDownloadToFileA, DownloadToFileA, and ShellExecuteA. This suggests the macro's purpose is to download and run a secondary payload. The specific strings extracted are the most critical IOCs for this analysis.

Heuristics 2

  • Excel 4.0 macro sheet (1 sheet(s)) critical OOXML_XLM_MACROSHEET
    Spreadsheet contains an Excel 4.0 (XLM) macro sheet — XLM was a major Office malware vector during 2020-2022 and evaded many VBA-focused controls before Microsoft tightened XLM defaults. Even legitimate XLM use is rare in modern workbooks. The macro sheet is stored as XLSB/BIFF12 binary content, which many XML-only OOXML scanners miss.
  • Binary XLM macro sheet with WinAPI/download strings critical OOXML_XLM_BINARY_WINAPI_STRINGS
    Excel 4.0 macro sheet is stored as BIFF12/XLSB binary data and contains Win32 download or process-execution API strings such as URLDownloadToFileA, ShellExecuteA, or CreateDirectoryA. These strings are high-signal in XLM macro sheets and catch payload-download macros that XML-formula scanners cannot parse.

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
99a6a52acb8f5c734f6d86faf89e0637a94ac99f953aa583d2658b47d2e1f9b9		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 194023 bytes

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